Post-translational modifications on the lysine chains of histones are a major way by which chromatin structure is modified to regulate gene expression. Methylation and acetylation are examples of such chemical modifications. A number of enzymes that effect histone modifications have been discovered and due to their effects on gene expression and cellular function, they have been targeted for therapeutic intervention. LSD1 is a histone demethylase that uses flavin adenine dinucleotide (FAD) as cofactor. Methylated histones H3K4 and H3K9 have been shown to be targets of LSD1. Other non-histone substrates include p53, E2F1, DNMT1 and STAT3.
LSD1 consists of three major domains: The N-terminal Swi3-Rsc8-Moira (SWIRM) domain which functions in nucleosome targeting, the tower domain which participates in protein-protein interactions and the C-terminal catalytic domain that has similarity to the monoamine oxidases. LSD1 also shares homology with another lysine demethylase LSD2 but it is very distinct from the Jumomji type histone demethylases. The enzymatic activity of LSD1 is dependent on the redox process of FAD and the protonated nitrogen in the methylated lysine is thought to limit its activity to mono- and di-methylated lysines in position 4 or 9 of histone H3 (H3K4 or H3K9).
LSD1 has been reported to be involved in a number of biological processes, including cell proliferation, epithelial-mesenchymal transition, stem cell biology and malignant transformation of cells. It has also been shown to be involved in cell differentiation. LSD1 has been implicated in a number of myeloproliferative and lymphoproliferative diseases such as acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). It has also been shown to be linked to the aberrant function of the androgen receptor in prostate cancer as well as other cancers such as Small Cell Lung cancer. Reviews describing a variety of reversible and irreversible LSD1 inhibitors were published by Mould, Daniel P., et al., “Reversible Inhibitors of LSD1 as Therapeutic Agents in Acute Myeloid Leukemia: Clinical Significance and Progress to Date,” Med. Res. Rev., 35, No. 3, 586-618, (2015); and Xheng, Yi-Choa, et. al., “A Systematic Review of Histone Lysine-Specific Demethylase 1 and Its Inhibitors” Med. Res. Rev., 35, No. 5, 1032-1071, (2015). Therefore, LSD1 has been a target for anti-cancer drug discovery.
As a drug discovery target, LSD1 has a fair degree of structural similarity to the Flavin-dependent Monoamine oxidases (MAOs). Both LSD1 and Monoamine oxidases utilize FAD as cofactor, e.g., as reported by G. W. Humphrey et. al., “Stable Histone Deacetylase Complexes Distinguished by the Presence of SANT Domain Proteins CoREST/kiaa0071 and Mta-L1” J. Biol. Chem, 276, 6817-6824 (2001) and Shi, et. al., “Coordinated histone modifications mediated by a CtBP co-repressor complex” Nature, 422, 735-738(2003). Thus a number of MAO inhibitors have been shown to inhibit LSD1 through irreversible interaction of FAD. Attempts have also been made to discover reversible inhibitors of LSD1.
In summary, LSD1 provides a pharmacological target for cancer and other disorders that associate with LSD1's activity. In particular, the need exists for novel small molecules that inhibit the activity of LSD1, which includes both irreversible and reversible inhibitors.